The digital display mode of a measured time interval offers greater reading comfort than the analogue mode, particularly during practice of a sporting activity. Chronograph watches with a digital display are known to those skilled in the art. They generally include a chronograph mechanism including a chronograph train carrying a measured time seconds hand, or chronograph hand, and a counter mechanism with discs. The display of measured time by discs is either of the continuous or instantaneous type. A continuous display means a display created by the slow movement of figures through an aperture, and an instantaneous display means a display by jumps passing from one unit or ten, to the next unit or ten.
An example of a continuous digital display chronograph watch is given in FR Patent Application No. 2 097 126. It concerns a chronograph watch fitted with a measure time seconds hand, a minute indicator disc visible through a first aperture, and an hour indicator disc visible through a second aperture. The energy for driving the discs is provided by the barrel of the basic movement, via a transmission train that can be uncoupled. Driving is continuous such that the energy consumption of the counter mechanism is low. The barrel of the basic movement is thus enough to supply the movement and the chronograph mechanism with energy. However, the continuous display is inconvenient and means that the measured time cannot be read at a glance.
A chronograph watch with an instantaneous digital display is presented in EP Patent No. 1 498 788. Said watch includes a basic movement powered by a first energy source, and a chronograph mechanism provided with a measure time seconds hand, and three indicator discs respectively for the minute units, tens of minutes and hours. Each of the discs is positioned by a jumper spring and the elastic force of the spring has to be overcome at each jump in order to drive it through steps. Consequently, the energy consumption of this mechanism is high and cannot be taken from the energy source of the basic movement. In order to overcome this drawback, the chronograph mechanism has three additional energy sources each powering one indicator disc. This solution considerably increases the complexity and space requirement of the chronograph mechanism, and thereby increases the manufacturing costs.